Blood smeared slide centrifuge

ABSTRACT

In the preparation of blood films for microscopic examination a slide spins in a centrifuge for a time which is a function of the red blood cell concentration of the blood. A drive circuit controls the time of spinning of a slide centrifuge. A variable control for the centrifuge motor includes a manual adjustment which is adjustable across a scale labeled as a function of the percent hematocrit of the blood.

United States Patent 1191 Amos et al.

[451 Sept. 23, 1975 1 1 BLOOD SMEARED SLIDE CENTRIFUGE [75] Inventors: Lynn G. Amos, Raleigh, NC;

James W. Bacus, Hinsdale, 111.; Robert C. Beaty; Charles II. Rogers, both of Raleigh, N.C.

[73] Assignee: Corning Glass Works, Corning,

[22 Filed: May24, 1973 21 Appl. No.1 363,433

[52] US. Cl. 118/6; 118/52; 23/2585; 73/614, 117/3; 117/101; 233/1 R [51] Int. C1. B0413 9/10; GOlN 1/28; G02B 21/34 [58] Field of Search 118/6, 7, 11,54, 52, 55, 118/53, 56, 9, 10; 117/3, 101', 23/230 B, 259,

[56] References Cited UNITED STATES PATENTS 2,908,907 10/1959 Danielsson 233/26 3,402,883 9/1968 Romer 233/26 3,415,627 12/1968 Rail 23/259 3,567,113 3/1971 Stansell et a1 233/26 3,695,911 10/1972 Polin 117/101 3,705,048 12/1972 Staunton 117/3 3,720,368 3/1973 Allen 233/26 3,730,760 5/1973 Machmiller 117/101 3,750,941 8/1973 Drucker 233/26 FOREIGN PATENTS OR APPLICATIONS 1,938,603 2/1971 Germany 117/101 Primary ExaminerCharles E. Van Horn Assistant Examiner.l. Gallagher Attorney, Agent, or Firm-Walter S. Zebrowski; Clarence R. Patty, Jr; Richard E. Kurtz [57] ABSTRACT In the preparation of blood films for microscopic examination a slide spins in a centrifuge for a time which is a function of the red blood cell concentration of the blood. A drive circuit controls the time of spinning of a slide centrifuge. A variable control for the centrifuge motor includes a manual adjustment which is adjustable across a scale labeled as a function of the percent hematocrit of the blood.

11 Claims, 9 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of 3,906,890

wao Ow 10:25 HEO ZO US Patent Se t. 23,1975 sheath 3,906,890

l PLATEN WITH RECESS FOR SLIDE MOTOR SHAFT TIME (SEC) 5 0.0 i s I l0 I5 3O 4O HEMATOCRIT ('7) US Patent Sept. 23,1975 Sheet 5 M6 3,906,890

MANUAL TIMER STA RT US Patent Sept. 23,1975 Sheet 6 of 6 3,906,890

BLOOD SMEARED SLIDE CENTRIFUGE BACKGROUND OF THE INVENTION This invention relates to methods of, and apparatus for, preparing a blood smeared slide for analysis and more particularly to spinning the slide for a time which is a function of the red cell concentration of the blood.

In the analysis of blood samples, the blood is smeared on a laboratory slide and the smear is stained. By counting the leukocytes on the stained smear, laboratory technicians perform what is referred to as a white blood cell differential. Automation of this differential has significant economic impact because the differential is performed so frequently at every hospital. A thesis by .l. W. Bacus, An Automated Classification of the Peripheral Blood Leukocytes by Means of Digital Image Processing, University of Illinois, Chicago, 197], describes one automated system.

Copending application Ser. No. 353,004 filed Apr. 20, I973 Douglas A. Cotter, Image Scanning Converter for Automated Slide Analysis describes a sys tem developed by my co-workers for automatically scanning and determining the relative number of different types of leukocytes on the stained smear.

Centrifugally spinning a blood wetted slide to pro duce a monolayer blood film is described in a paper by M. Ingram and F. M. Minter, Semi-automatic Prcpa ration of Coverglass Blood Smears Using A Centrifugal Device," Amer. J. Clin. Path I: 2l422l, 1969. The method described in this paper includes flooding a coverglass with a layer of blood and centrifuging the cover glass rapidly in a plane parallel to the plane of rotation of the centrifuge, Excess blood is spun off leaving a monolayer of well spread blood cells on the cover glass.

Centrifuges for spinning blood smeared slides are commercially available. Such devices are available from: Plat General Corporation, (sold by PIE, Inc. 947 Old York Rd., Abington, Pennsylvania); Perkin-Elmer Corp., 50 Danbury Rd., Wilton, Conn.; and Shandon Scientific Co. Inc., 515 Broad St., Sewickley, Pennsylvania.

While some commercially available blood spinning apparatus have controls for adjusting the spin time, it has been the practice to set this spin time to one position and to allow it to remain there for all blood slide preparations.

After use of the centrifuges and blood spinning techniques described above, we have made the following observations.

The separation of the red cells was not the same for all blood samples. For some bloods the spinning resulted in blood films with sparsely populated areas interspersed with clumps of cells. For other bloods the technique produced a slide with overlapping cells.

As mentioned in the article by Ingram, the morphology of the red cells was often altered. The cells appeared overly flattened and noncircular. Often, white blood cells (specifically neutrophils) appeared damaged.

For the blood film to be uniform, a large quantity of blood had to be used. Typically, the surface was flooded prior to spinning. If the entire surface was not wetted an irregular sunburst" pattern of the blood resulted.

Manual methods for obtaining a blood smear (wedge and cover-slide method) require a skilled operator, are not very reproducible, and produce distributions which are nonuniform, often containing a high percentage of damaged cells.

U.S. Pat. Nos. 3,577,267 Preston et al. and 3,705,048 Staunton describe centrifuges which can be used to prepare blood slides but the apparatus described in these patents does not solve the problem of producing blood smears with good cell morphology and good cell distribution for all blood samples.

Accordingly, we have concluded that the preparation of a slide which is suitable for an automated white cell differential is a critical task which must be performed by a machine operated by an operator who need not make subjective judgments in order to get reproducible results.

SUMMARY OF THE INVENTION In accordance with our invention blood films with good cell morphology and good cell distributions are produced by centrifuging the slide at a constant rotational velocity for a short period of time determined as a function of the red cell concentration.

In accordance with this invention apparatus for preparing a blood slide includes a centrifuge for spinning the slide and a drive circuit for controlling the time of spinning of the centrifuge. A variable control for the drive circuit is manually adjustable across a scale labeled as a function of the red blood cell concentration of the blood. In using this apparatus the operator observes the hematocrit (percent of blood volume occupied by red blood cells) either through tests or through observation. The operator sets the manual control to the indicated percent hematocrit of the blood. When the apparatus is started. the spin time is automatically adjusted in accordance with the blood hematocrit.

The foregoing and other objects, features and advantages of the invention will be better understood from the following more detailed description and appended claims.

DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram of the blood spinning apparatus of this invention;

FIG. 2 shows the platen and a blood slide;

FIG. 3 is a pictorial view of the apparatus;

FIG. 4 shows hematocrit as a function of spin time;

FIG. 5A depicts a blood slide which has been centrifuged for too long a time;

FIG. SB depicts a blood slide which has been centrifuged for approximately the correct time; and

FIG, SC depicts a blood slide which has not been centrifuged sufficiently long;

FIG. 6 is a schematic diagram of the variable control; and

FIG. 7 is a schematic diagram of the drive circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1 and 2 the blood smeared slide II is positioned in a recess in a platen 12. The platen is fixed to the output shaft of a high torque, low inertia, DC motor 13.

A drive circuit 14 control the motor 13. A variable control 15 for the drive circuit includes a variable resistor which is adjusted in relationship to a scale labeled as a function of the red blood cell concentration of the blood. A start switch 16 starts the centrifuge motor which is rapidly accelerated to a selected rotational velocity. The motor is maintained at this selected velocity for a period of time determined by the variable control 15.

Two safety interlock switches 17 and 18 are actuated by a lid which covers the centrifuge. The centrifuge motor runs only when the lid is closed. This is a safety feature which prevents the slide from scaping the confines of the machine in the unlikely event of the slide slipping out of the recess in the platen.

An on-off switch 19 applies power to the drive circuit 14.

FIG. 3 depicts the housing 20 for the apparatus. It includes a hinged lid 23 which provides access to the platen. The hinged lid 23 actuates the safety interlock switches 17 and 18.

A start button 21 is provided to start the spin motor. The knob 22 adjusts the variable control in accordance with a scale labeled in hematocrit percent.

FIG. 4 shows spin time as a function of blood hematocrit which we have found to be a good measure of the red blood cell concentration. Good films can be obtained by spinning slides at a constant velocity for a period of time which is a linear function of the hematocrit. Other measures of red blood cell concentration could be used. For example. hemoglobin concentration could be used as the measure. It is important that the centrifugal forces be applied to the blood longer. or in greater amounts. for increased red blood cell concentration. Therefore. the spin time can be held constant and the rotational speed can vary as a function of red blood cell concentration. Spin speed should be optimized to avoid altering the cell morphology. We have found that more damage to the cells occurs at high spin speeds than at lower spin speeds. By providing a rapid acceleration up to the final spin speed (requiring only ZOU-3UO milliseconds) a motor speed of 5.0M) RPM. can be used. At this speed the time can be adjusted as shown in FIG. 4 to obtain a good monolayer of blood.

FIG. 5A depicts a microscope slide which has been centrifuged at too high a speed or for too long a time. The conventional red blood cell morphology has been destroyed. most cells being overly flattened or spread out. (In FIGS. 5A. B and C for convenience. only a portion of the slide has been depicted as blood smeared. Actually after centrifuging the entire slide should be uniformly coated.) FIG. 5B depicts a slide which has been correctly centrifuged. The conventional blood cell morphology is retained. In FIG. 5C the cell distri bution is much too closely packed as a result of spinning for too short a time or at too low a speed.

Often. the operator has available an analysis of the blood giving the percent of hematocrit in the blood. However. it is possible to estimate low. normal or high values of heniatocrit based on the redness of the blood when cxact percentages are not available.

FIG. 6 shows the variable control for adjusting the time of spinning. When the start button 24 is pushed the capacitor 25 is discharged. This turns the transistor 26 on. This in turn discharges capacitor 27. lmmedi ately the output of the operational amplifier 28 goes to the positive lcvel. Because resistor 29 is large. the transistor 26 cannot remain on after the capacitor 25 has been discharged. Consequently. transistor 26 is turned off allowing capacitor 27 to be recharged through the variable resistor 30. When the voltage v applied to the input of operational amplifier 28 returns to the lev cl V. the output returns to a low level. This stops the motor. By varying the resistor 30 the time of the recharge and hence the time that the motor runs can be changed. The resistor 30 is disposed in relationship to a scale calibrated in percent hematocrit of the blood.

Another variable resistor 31 changes the input voltage to the motor drive circuit thereby prot iding a speed control. The output to the motor driver circuit is provided by the transistor 32.

FIG. 7 shows the motor drive circuit. The input to this circuit comes from the control circuit of FIG. 6. The input is applied to the amplifier 33 whose output drives the DC motor 34.

Amplifier 35 develops a signal proportional to the negative of !'R voltage drops in the motor. Resistors 36, 39 and 40 combine the output of amplifier 35 and the potential applied to the motor to yield a measure of back EMF which is directly proportional to motor speed. This feedback signal is then applied to the negative input of operational amplifier 33.

Transistors 37 and 38 provide the actual motor drive current. The operation is as follows. When the input from the drive circuit is positivthc motor 34 runs at a speed dependent on the voltage of the input signal. When the input voltage is zero the motor stops. Amplifier 33 compares the desired spced. at the positive input. with the actual speed as indicated by the back EMF signal applied to the negative input. The output of operational amplifier 33 is an error signal which turns the transistor 37 on to accelerate the motor or it turns transistor 38 on to de-accelcrate the motor.

Summarizing. when the start button is pushed the input to the circuit of FIG. 7 goes positive. This turns on transistor 37 to provide a high voltage surgc that brings the motor 34 up to a desired speed in a short period of time. The operational amplifier 35 and associated resistors sense the back EMF of the motor and develop a feedback signal proportional to actual motor speed. This is applied in a feedback loop which drives the motor at the regulated spin speed. When the input to the circuit of FIG. 7 returns to the Zero level. the transistor 38 is turned on. This applies a reverse polarity current to the motor 34 to bring the motor to a stop in a short period of time.

While a particular embodiment of the invention has been shown and described various modifications are within the true spirit and scope of the invention. The appended claims are. therefore. intended to cover such modifications.

What is claimed is:

l. Apparatus for preparing blood films on a microscope slide comprising:

a centrifuge for spinning said slide with a surface of said slide perpendicular to the spin axis of said centrifuge.

a drive circuit for said centrifuge for controlling the time integral of the centrifugal force applied to the slide by said centrifuge.

a manually-adjustable variable control for said drive circuit for adjusting said time integral. and

a scale having indicia corresponding to red blood cell concentration and associated with said variable control for indicating the desired setting thereof as a function of red blood cell concentration.

2. The invention defined in claim 1. wherein the said manually adjustable variable control is operative to adjust the time of spinning.

3. The apparatus recited in claim 2 wherein said centrifuge comprises:

a platen having a recess for holding said slide.

a high torque. low inertia motor. said platen being fixed to the output shaft of said high torque. low inertia motor.

4. The apparatus recited in claim 2 wherein said drive circuit includes:

means for providing a high voltage surge that brings said motor up to a desired speed in a short period of time,

means for sensing the back EMF of said motor to drive it at a regulated spin speed. and

means for applying a reverse polarity current to said motor to brake the motor to a stop in a short period of time.

5. The apparatus recited in claim 2 wherein said variable control comprises:

a manually adjustable resistor connected in said motor drive circuit. and

said scale is calibrated in percent hematocrit of the blood and disposed in relation to said manually adjustable resistor.

6. The apparatus recited in claim 2 further comprising:

a housing for said apparatus with a hinged lid for access to said platen. and

an interlock switch in series with said drive circuit. said interlock switch being actuated by said lid so that said lid must be closed before said motor can be energized.

7. The invention defined in claim I, wherein the time of spinning remains fixed and said manually-adjustable variable control is operative to adjust the rate of spinning.

8. The apparatus recited in claim 7 wherein said centrifuge comprises: 5 a platen having a recess for holding said slide.

a high torque. low inertia motor, said platen being fixed to the output shaft of said high torque. low inertia motor.

9. The apparatus recited in claim 7 wherein said drive 10 circuit includes:

means for providing a high voltage surge that brings said motor up to a desired speed in a short period of time,

means for sensing the back EMF of said motor to drive it at a regulated spin speed. and

means for applying a reverse polarity current to said motor to brake the motor to a stop in a short period of time.

10. The apparatus cited in claim 7 wherein said vari- 20 able control comprises:

a manually adjusted resistor connected in said motor drive circuit. and said scale is calibrated in percent hematocrit of the blood and disposed in relation to said manually adjustable resistor.

ll. The apparatus recited in claim 7 further comprising:

a housing for said apparatus with a hinged lid for ac cess to said platen. and

an interlock switch in series with said drive circuit, said interlock switch being actuated by said lid so that said lid must be closed before said motor can be energized. 

1. Apparatus for preparing blood films on a microscope slide comprising: a centrifuge for spinning said slide with a surface of said slide perpendicular to the spin axis of said centrifuge, a drive circuit for said centrifuge for controlling the time integral of the centrifugal force applied to the slide by said centrifuge, a manually-adjustable variable control for said drive circuit for adjusting said time integral, and a scale having indicia corresponding to red blood cell concentration and associated with said variable control for indicating the desired setting thereof as a function of red blood cell concentration.
 2. The invention defined in claim 1, wherein the said manually adjustable variable control is operative to adjust the time of spinning.
 3. The apparatus recited in claim 2 wherein said centrifuge comprises: a platen having a recess for holding said slide, a high torque, low inertia motor, said platen being fixed to the output shaft of said high torque, low inertia motor.
 4. The apparatus recited in claim 2 wherein said drive circuit includes: means for providing a high voltage surge that brings said motor up to a desired speed in a short period of time, means for sensing the back EMF of said motor to drive it at a regulated spin speed, and means for applying a reverse polarity current to said motor to brake the motor to a stop in a short period of time.
 5. The apparatus recited in claim 2 wherein said variable control comprises: a manually adjustable resistor connected in said motor drive circuit, and said scale is calibrated in percent hematocrit of the blood and disposed in relation to said manually adjustable resistor.
 6. The apparatus recited in claim 2 further comprising: a housing for said apparatus with a hinged lid for access to said platen, and an interlock switch in series with said drive circuit, said interlock switch beinG actuated by said lid so that said lid must be closed before said motor can be energized.
 7. The invention defined in claim 1, wherein the time of spinning remains fixed and said manually-adjustable variable control is operative to adjust the rate of spinning.
 8. The apparatus recited in claim 7 wherein said centrifuge comprises: a platen having a recess for holding said slide, a high torque, low inertia motor, said platen being fixed to the output shaft of said high torque, low inertia motor.
 9. The apparatus recited in claim 7 wherein said drive circuit includes: means for providing a high voltage surge that brings said motor up to a desired speed in a short period of time, means for sensing the back EMF of said motor to drive it at a regulated spin speed, and means for applying a reverse polarity current to said motor to brake the motor to a stop in a short period of time.
 10. The apparatus cited in claim 7 wherein said variable control comprises: a manually adjusted resistor connected in said motor drive circuit, and said scale is calibrated in percent hematocrit of the blood and disposed in relation to said manually adjustable resistor.
 11. The apparatus recited in claim 7 further comprising: a housing for said apparatus with a hinged lid for access to said platen, and an interlock switch in series with said drive circuit, said interlock switch being actuated by said lid so that said lid must be closed before said motor can be energized. 